In the interests of the environment, and to comply with increasingly stringent regulatory demands, it is necessary to increase the amount of biofuels used in automotive fuels.
Biofuels are combustible fuels derived from biological sources, which result in a reduction in “well-to-wheels” (ie from source to combustion) greenhouse gas emissions. In gasoline fuels for use in spark ignition (petrol) engines, the most common biofuels are alcohols, in particular ethanol. These are typically blended with more traditional gasoline fuel components. However, the disruption of hydrogen-bonding when ethanol is combined with gasoline hydrocarbons results in an undesirable increase in the vapour pressure of the fuel. Ethanol also impacts the distillation properties of gasoline fuels, increasing their E70 and E100 values. As a result, a gasoline base fuel typically has to be specially reformulated if it is to be blended with ethanol, to ensure that the resultant blend meets gasoline specifications around the world. This reformulation naturally increases the cost and complexity of the fuel manufacturing process, and can limit the concentration at which ethanol can practically be included in gasoline fuels.
It is also known to include certain monoterpenes as biocomponents in gasoline fuels. These include monocyclic monoterpenes such as limonene, α- and β-phellandrene, α- and γ-terpinolene and γ-terpinene, and bicyclic monoterpenes such as α-pinene, β-pinene, 3-carene and α-fenchene, which are present in gum turpentine and crude sulphate turpentine produced by the wood pulping industry. Such monoterpenes have boiling points within the normal gasoline boiling range. However they have relatively low research octane numbers (RONs) and in particular motor octane numbers (MONs), and in addition they tend to have poor oxidative stability due to the degree of unsaturation in their molecules. These properties together make them less well suited for use in gasoline fuels.
It would be desirable to provide new biofuel-containing gasoline fuel formulations that could overcome or at least mitigate the above problems.